Towing mirrors and convex blind spot mirrors: how to choose, set up and use them safely
Find out when to add mirrors, what laws require and how to aim them for towing
Safety Behind the Wheel Foundation built this guide from federal mirror standards, National Highway Traffic Safety Administration (NHTSA) and Federal Motor Carrier Safety Administration (FMCSA) guidance, Insurance Institute for Highway Safety (IIHS) research, state mirror laws and published mirror research. Every source is listed at the end.
What supplemental and towing mirrors do
Factory mirrors are designed for the vehicle by itself. Hitch a wide camper, load a tall cargo box or drive a van with no rear windows, and part of that view disappears. Supplemental and towing mirrors give it back.
Their main job is visibility and awareness. You need to know what is beside and behind you before you change lanes, merge, turn or back up. The federal mirror standard exists to reduce deaths and injuries that happen when drivers cannot see clearly to the rear [5].
The main types
- Flat mirror. Federal rules call this “unit magnification.” It shows objects at true size, so it gives the best sense of distance.
- Convex mirror. The glass bulges outward. It shows a wider area, but everything looks smaller.
- Spot or blind spot mirror. A small convex mirror that sticks onto or clips beside your main mirror.
- Clip on towing mirror. An extension that straps over your existing mirror and comes off when you stop towing.
- Replacement towing mirror. A full unit that replaces the factory mirror. Many slide or flip out for towing.
- Rear crossview mirror. A convex mirror on a back corner of a box truck. It shows the area right behind the vehicle.
People who tow campers, boats and utility trailers use these mirrors. So do drivers of moving trucks and delivery vans. Fleet owners fit them to work vehicles, and repair shops install and replace them.
Why a curved mirror changes how far away things look
A convex mirror works a bit like a fish eye lens. The curve squeezes a wide scene onto a small piece of glass. That is how it can show a car that a flat mirror would miss. But the car looks smaller, and your brain reads “smaller” as “farther away.”
That is why a car’s convex passenger side mirror must carry the warning “Objects in Mirror Are Closer Than They Appear” [5]. The federal standard also limits how sharply that mirror may curve, to a radius of about 35 to 65 inches [5]. The tighter the curve, the smaller things look. A tiny spot mirror that shows a wide angle must curve sharply, so its images are very small.
What research shows
- In a real world test, distance estimates in convex mirrors were right on average but varied much more from one judgment to the next [6].
- The same study looked at time to contact, meaning the seconds left before a car behind reaches you. People judged it best with no mirror at all [6].
- Later lab tests found viewers could partly correct for a curved mirror’s distortion, but only up to a point [7].
- When the mirror sat farther from the viewer’s eyes, people thought an approaching car would arrive later than it really would [7]. Extended towing mirrors sit farther out, so leave extra room.
- In a simulator, car drivers and expert truck drivers reacted more slowly to objects seen only in mirrors set far off to the side than to objects seen through the windshield [8].
The research boils down to one rule. Use the flat glass to judge distance and speed. Use the convex glass to learn whether something is there. Then confirm with a second look or a head check before you move.
When you need more mirror than you have
Here is a quick test. Sit in your normal driving position with the trailer hitched. If you cannot see down both sides of the trailer to the road behind it, your mirrors are not wide enough.
Comparison compiled by Safety Behind the Wheel Foundation
Mirror options for common towing and hauling setups
| Situation | What gets blocked | Mirror options to consider |
|---|---|---|
| Camper or trailer wider than your vehicle | Lanes beside and behind the trailer | Towing mirrors that reach past the trailer |
| Boat or utility trailer narrower than your vehicle | Low objects and rear corners | Factory mirrors may work. Add spot mirrors |
| Pickup with a slide in camper or tall load | The inside rearview mirror | Two outside mirrors aimed at both sides |
| Delivery van with no rear windows | Inside mirror and right rear corner | Large side mirrors with convex sections, plus a camera |
| Box truck or moving truck | Everything right behind | Convex sections, a rear crossview mirror and a spotter |
Even a narrow trailer can hide a motorcycle or a child walking behind it. Walk around the whole rig before you move.
What the rules say about mirrors
Federal standards tell manufacturers what new vehicles must have. Federal motor carrier rules cover commercial trucks and buses. State traffic laws set what every driver on the road must have.
Federal rules
Federal Motor Vehicle Safety Standard (FMVSS) 111 sets mirror rules for new vehicles. A passenger car needs an inside mirror and a flat outside mirror on the driver’s side [5]. The passenger side mirror may be flat, or convex with the warning label [5].
Trucks and multipurpose vehicles rated between about 10,000 and 25,000 pounds fully loaded need flat outside mirrors on both sides [5]. Each needs at least 323 square centimeters of glass, about 50 square inches, on a stable, adjustable mount [5].
Federal motor carrier rules require each covered bus, truck and truck tractor to have two outside mirrors firmly attached, one on each side, showing the road behind, with a few exceptions [9]. Before driving, a commercial driver must be satisfied the mirrors are in good working order [10].
Federal law also bars dealers, rental companies and repair businesses, among others, from knowingly disabling safety equipment installed to meet a federal standard [11]. That is a good reason to make sure a new or add on mirror keeps the view the original gave.
State examples, as of October 2026
The common thread in state laws is a clear view of the road behind you. Several states measure that view at 200 feet [1, 2, 3].
- Washington requires a left side mirror and a second mirror, inside or on the right, each showing at least 200 feet behind [1]. Delivery trucks registered or based there with a walk in cargo box up to 18 feet long need a rear crossview mirror or backup device [1].
- Minnesota requires a mirror or other technology showing at least 200 feet behind when a vehicle’s design, its load or a connected vehicle such as a trailer blocks the rear view [2].
- Florida requires every vehicle, alone or towing, to have a mirror showing at least 200 feet behind [3]. A violation is a noncriminal, nonmoving traffic infraction [3].
- Michigan requires a mirror when a vehicle’s design or load blocks the rear view, and commercial vehicles of half ton capacity or more need one on each side [12]. Outside mirrors do not count toward a vehicle’s legal width there [12].
Other countries take a similar view. The United Kingdom tells drivers to fit towing mirrors when a trailer is wider than the back of the car [13]. Towing there without proper mirrors can mean a fine of up to 1,000 pounds sterling and 3 penalty points [13].
How to choose supplemental or towing mirrors
Start with the gap you need to fill, not the product. A camper wider than your truck calls for towing mirrors. A van with a blind right rear corner may only need a well placed convex mirror. Whatever you add, keep the original flat view usable.
Comparison compiled by Safety Behind the Wheel Foundation
Supplemental and towing mirror types compared
| Type | Good fit for | Watch for |
|---|---|---|
| Clip on towing mirror | Occasional towing and rentals | Slipping, shaking, scuffed paint |
| Replacement towing mirror | Frequent towing | Cost, plus wiring for heat and signals |
| Stick on spot mirror | Small gaps on cars and vans | Tiny images, and it covers some flat glass |
| Rear crossview mirror | Box trucks and delivery vans | Needs regular aiming and does not replace a spotter |
Where to get mirrors and who should install them
Auto parts stores carry clip on extensions and spot mirrors. The vehicle dealer’s parts department can tell you whether your model offers factory towing mirrors. Trailer and camper dealers often stock towing mirrors. Truck equipment installers and qualified repair shops fit mirrors on work trucks and vans.
Most owners can put on a clip on mirror by following the instructions. A replacement towing mirror may mean removing a door panel and connecting wiring. If your mirror holds a camera or sensor, ask the installer whether that system needs to be checked afterward.
Fleet owners should set one mirror standard for each vehicle type. After a collision or mirror strike, ask the shop to replace damaged mirrors with parts that match the original view and features.
Set up your mirrors before every trip
Mirrors only help if they are aimed for today’s load. This routine works for most trailers and large vehicles.
- Park on level ground with the trailer hitched and straight behind you.
- Set your seat and steering wheel, then sit in your normal driving position.
- Slide or flip towing mirrors out and make sure they lock.
- Aim each flat mirror so the trailer’s side barely shows at the inner edge.
- Aim each convex section at the next lane and the trailer’s rear wheels.
- Have a helper walk back along each side and into the next lane. Note where the helper drops out of view.
- Check that the mirrors do not shake with the engine running.
- Recheck the aim after the first few miles and after each stop.
Repeat the helper walk whenever you change trailers or loads. A different trailer moves every gap.
Driving and backing with extra mirrors
Good mirrors still need good habits. Federal safety officials advise truck and bus drivers to check their mirrors every 8 to 10 seconds [14]. That steady rhythm works when you tow, too. Safety Behind the Wheel Foundation gives every driver who tows the same advice.
For lane changes, find the gap in the convex glass, then judge its size in the flat glass. Signal early, check again and move over slowly. A trailer needs a much bigger gap. The Drive With Care guide to lane changes and blind spots covers a full routine.
In turns, watch the trailer’s wheels in the convex mirror. They track inside your path and can strike curbs or people. Extended mirrors add width, so fold them in when you unhitch.
When backing, go slowly and use both mirrors. Get out and look if you are unsure. Keep a spotter in a mirror at all times, and stop if you lose sight of them.
Technology is a backup. Blind spot warning alerts you to vehicles in the next lane you may not see [4]. It has been shown to cut lane change crashes by 14 percent [15]. Backup cameras help, but they do not replace mirrors or turning to look [4]. A trailer can change how these systems work, so check your owner’s manual. You, not the system, are responsible for driving [4].
Common mistakes and limits
- Covering the flat glass. A spot mirror in the middle of your flat mirror hides your best distance view. Put it at an outer corner.
- Judging distance in convex glass. Cars in it are closer than they look.
- Loose clip ons. A shaking mirror gives a blurry picture. Check straps at every stop.
- Forgetting the extra width. Extended mirrors can hit mailboxes, gas pumps and people.
- Trusting the inside mirror. If cargo fills the back window, it shows nothing useful.
- Trusting a camera alone. Cameras can be dirty, fogged or aimed too narrowly.
Keep mirrors clean, tight and working
Clean mirror glass with a soft cloth. Clear ice gently, and skip metal scrapers on mirror glass. Test heaters, turn signals and power adjustment before each trip.
Check that folding joints click into place and sliding arms lock. Replace cracked, peeling or cloudy glass. After a mirror strike, look for hidden cracks in the housing and mount.
For fleets, put mirrors on the daily vehicle check, as commercial drivers must already do [10]. You can also look up recalls on your vehicle and aftermarket mirrors at NHTSA’s recall search.
Frequently asked questions
Are clip on towing mirrors as good as replacement towing mirrors?
Both can work if they fit well and stay solid. Clip ons cost less and suit occasional towing or a rental trailer. Their weak point is the mount, which can slip or shake at speed. Replacement towing mirrors take the place of the factory mirrors and tend to stay steadier. They cost more and may need wiring work. If you tow often, a replacement set is worth a look.
Do I need towing mirrors for a small utility trailer?
Not always. If the trailer is narrower than your vehicle and you can still see the road on both sides of it, factory mirrors may be enough. Check with the trailer hitched, using a helper. If the trailer or its load hides the lane beside you or the road behind, add mirrors. Some states require a clear view at least 200 feet back [1, 2, 3].
Why do cars look farther away in my passenger side mirror?
On many cars, that mirror is convex. It curves outward to show a wider area, which makes everything look smaller. Your brain reads smaller as farther. That is why federal rules require the warning that objects are closer than they appear [5]. Use that mirror to spot a vehicle, then check your flat mirror and turn your head before you move over.
Where should I put a stick on blind spot mirror?
Most drivers place it at an upper or lower outer corner of the side mirror. That spot fills the gap beside your rear fender without hiding much of the flat view. Sit in your normal position and have a helper walk beside your car to find the best spot before you stick it down. Avoid covering the center of the flat glass.
What should a fleet manager check on vans and trucks?
Start with a written mirror setup for each vehicle type, including any convex or rear crossview mirrors. Make mirror checks part of the daily inspection, which commercial drivers must already do [10]. Teach drivers how to aim mirrors, and recheck the aim when drivers or loads change. Replace damaged mirrors quickly instead of running a vehicle with one missing.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges anyone who tows or hauls to make sure their mirrors show the road beside and behind the load before every trip. Supplemental and towing mirrors give back the view a trailer, camper or cargo box takes away. A flat mirror tells you how far away something is. A convex mirror tells you that something is there. You need both, and you need to know which is which.
Choose mirrors that fit your vehicle and the job, mount them solidly and aim them with the load attached. Then keep up the habits that make them work: steady scanning, a second look and a spotter when you back up.
Related articles
- Secure cargo and tow safely: a loading guide for families and trailers
- Lane changes and blind spots: a safe routine every driver can use
- Sharing the road with trucks and buses: No Zones, passing and stopping
- Parking lot, driveway and backing safety: beat your blind zones
- Work vehicle cargo, tools and trailers: how to secure every load
Sources and further reading
- 1Washington State Legislature. RCW 46.37.400, Mirrors, backup devices. Last amended 1998; accessed October 2026. apps.leg.wa.gov/rcw/default.aspx?cite=46.37.400
- 2Minnesota Office of the Revisor of Statutes. Minnesota Statutes 169.70, Mirrors. Amended 2023; accessed October 2026. revisor.mn.gov/statutes/cite/169.70
- 3Florida Legislature. Florida Statutes 316.294, Mirrors. 2026 Florida Statutes. leg.state.fl.us/…/0316.294.html
- 4National Highway Traffic Safety Administration (NHTSA). Driver Assistance Technologies. No update date shown; accessed October 2026. nhtsa.gov/…/driver-assistance-technologies
- 5Electronic Code of Federal Regulations (eCFR). 49 CFR 571.111, Standard No. 111; Rear visibility. Up to date as of October 1, 2026. ecfr.gov/…/section-571.111
- 6Hecht H, Brauer J. Convex rear view mirrors compromise distance and time-to-contact judgements. Ergonomics, 50(4):601-614 (via PubMed). Published April 2007. Data year: 2007 (experimental study). [https://pubmed.ncbi.nlm.nih.gov/17575717/](https://pubmed.ncbi.nlm.nih.gov/17575717/) (DOI [https://doi.org/10.1080/00140130601154954](https://doi.org/10.1080/00140130601154954)) doi.org/10.1080/00140130601154954
- 7Hahnel UJJ, Hecht H. The impact of rear-view mirror distance and curvature on judgements relevant to road safety. Ergonomics, 55(1):23-36 (via PubMed). Published 2012. Data year: 2012 (experimental study). [https://pubmed.ncbi.nlm.nih.gov/22176482/](https://pubmed.ncbi.nlm.nih.gov/22176482/) (DOI [https://doi.org/10.1080/00140139.2011.638402](https://doi.org/10.1080/00140139.2011.638402)) doi.org/10.1080/00140139.2011.638402
- 8Mole CD, Wilkie RM. Looking forward to safer HGVs: The impact of mirrors on driver reaction times. Accident Analysis and Prevention, 107:173-185 (via PubMed). Published September 2017. Data year: 2017 (simulator study). [https://pubmed.ncbi.nlm.nih.gov/28865992/](https://pubmed.ncbi.nlm.nih.gov/28865992/) (DOI [https://doi.org/10.1016/j.aap.2017.07.027](https://doi.org/10.1016/j.aap.2017.07.027)) doi.org/10.1016/j.aap.2017.07.027
- 9Electronic Code of Federal Regulations (eCFR). 49 CFR 393.80, Rear-vision mirrors. Current as of September 29, 2026. ecfr.gov/…/section-393.80
- 10Electronic Code of Federal Regulations (eCFR). 49 CFR 392.7, Equipment, inspection and use. Current as of October 1, 2026. ecfr.gov/…/section-392.7
- 11Legal Information Institute, Cornell Law School. 49 U.S. Code 30122, Making safety devices and elements inoperative. Accessed October 2026. law.cornell.edu/uscode/text/49/30122
- 12Michigan Legislature. Michigan Compiled Laws 257.708, Mirrors. Last amended 1978; accessed October 2026. legislature.mi.gov/…/MCL?objectName=mcl-257-708
- 13GOV.UK. Towing with a car: Trailers, caravans and towing equipment. Updated September 17, 2026. gov.uk/…/trailer-and-towing-equipment
- 14Federal Motor Carrier Safety Administration (FMCSA). Tips for Truck and Bus Drivers. Updated May 12, 2026. fmcsa.dot.gov/…/tips-truck-and-bus-drivers
- 15Insurance Institute for Highway Safety (IIHS). Advanced driver assistance. Updated September 2026. iihs.org/…/advanced-driver-assistance
This article reflects the safety priorities of towing safety and rear visibility. It is general education about mirrors and road safety, not legal, insurance or other professional advice. Mirror rules differ by state and change, so verify them with your state DMV, state patrol or legislature. Ask your vehicle dealer or a qualified installer about mirrors that fit your vehicle. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Towing mirrors and convex blind spot mirrors: how to choose, set up and use them safely.” drivewithcare.org, https://drivewithcare.org/towing-mirrors-convex-blind-spot-mirrors/. Reviewed October 2026.
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