What exactly is this tool intended to do?


Description is a bit mystifying. How and why would you use this thing?

Seriously? You use it to make the cut-out on car fenders bigger, to accommodate bigger tires; just like in the name, and the photos. I’ve never seen one, but its use is obvious.

Here’s a video of one in action. Pretty cool actually.

In the UK, your insurance would take a big hit for doing that. Is it the same in the US?

Also - I see rust problems down the line with water trapped in the fold.

How would your insurance company know, unless it was detected after a claim?

It looks like a Bop-It toy.

The traditional tool for this job is a baseball bat. Really.

You roll the bat through the gap between tire and fender lip as someone pushes or very slowly drives the car a few feet. By using first the old tires, then the new larger ones, and adjusting which section of the bat is used, and repeating the process, you can get a very smooth fender lip roll-in. Without even damaging the paint.

So this is all for a few millimeters of extra fender flare to accommodate the absolute fattest tire possible. Fascinating.

It comes mostly from restoration-modifying (“restomod”) muscle and pony cars, where a relatively small amount of folding up the inner flare lip can buy a lot of tire room. Not so much on smaller and newer cars where everything is already packed pretty tight and just lipping the fender won’t buy you clearance elsewhere.

It was common to universal in the classic Mustang set last time I looked - an hour with a cheap Louisville Slugger and a few friends (to push, drive and help drink the beer) and you could get substantially fatter tires under the fenders without rubbing, especially on a relatively sharp in-pointing flange. There is plenty of room inwards, fore and aft, and around the suspension… just not between the outer tire shoulder and the fender lip.

It can be considerably more than a few millimeters. An inch was normal, two or three inches with some work and care was possible, all without overtly reshaping the fender or actually putting in a “flare.”

No, if you want the absolute fattest rear tires possible you “tub” the rear wheel wells.

This involves cutting out the inner wheel well and welding in a larger tub that will gain room in the other direction, toward the center of the car. This usually involves shortening the rear axle also. Typically done only on drag racers but sometimes on lowriders and other custom mods.

And of course you can buy pre-made, weld-in tubs in various sizes.

Tubbing is almost entirely for stock-class drag racers, where the absolute maximum amount of rubber has to fit under standard body shell dimensions. It’s expensive, a major modification of chassis, body, suspension and driveline… and makes cars handle like absolute sh*t except in a straight line.

Lipping or flaring fenders to get more rubber on a more balanced basis, with more or less stock chassis, suspension geometry and a mostly-stock body shape, is a completely different approach to different ends.

I took an axe to my Jeep’s fender, but it had nothing to do with fitting larger tires.