Front wheel clearance

[Smifee]

Probably asked a million times but what's the clearance like on a front mount turbo? Looks like there a bit tight.. 

[clivegto]

Your not wrong 

[rerb]

I had more issues with the frame crossbars than the wheel/fender. I cut out the lower cross and had to shave away at the upper one to clear the wastegate actuator rod, this is with the proboost merge collector. Stock oil cooler lines also wouldn't play nice between the headers so I had to upgrade to stainless.

[Smifee]

I'm more worried about riding hard and the wheel hitting under braking, I'm a track racer so abuse the front end, thinking a under seat turbo maybe a better option

[clivegto]

12 minutes ago, Smifee said:

I'm more worried about riding hard and the wheel hitting under braking, I'm a track racer so abuse the front end, thinking a under seat turbo maybe a better option

When building your headers drop the forks through the yokes to check front wheel clearance. You can off set the turbo if needed or even grind a bit off.

First time I put one together then went for a test ride pressed the front brake and the front wheel locked up. Scarry shit, b12 kit on a 7.5 slabby. I quickly modified the headers to fit correctly 

 

[TLRS]

Forks bend too so make sure you have a little extra. If need be try fit something soft that wears very easy so you can verify the room required.

[TiZiK]

On 3/31/2023 at 6:09 PM, TLRS said:

Forks bend too so make sure you have a little extra. If need be try fit something soft that wears very easy so you can verify the room required.

How much you think forks actually bend?  Serious question.  I use old fork tubes as breaker bars and they are tough as nails.  I'm running a Holset HY35 on a slabby and also had to remove the crossbrace and shave down the other mount on the left side for proper clearence.  I have a good 1.5inches between the turbo and tire but this fork flex claim is always looming in the back of my head so I'm really curious about how much flex there actually is?

[Arttu]

I haven't ever tested this by myself but I recall estimations around 10mm from other people. So you should have at least that much clearance when the forks are fully compressed.

[imago]

38 minutes ago, Arttu said:

I haven't ever tested this by myself but I recall estimations around 10mm from other people. So you should have at least that much clearance when the forks are fully compressed.

You do hear figures and guesstimates from time to time for fork flex, but "How much do forks flex?" is like asking "How much will the power increase be if I fit a turbo?".

There are some obvious things involved, such as the larger the fork diameter the more resistant to flex they will be. Also things like USD forks are much more resistant to flex due to the much longer outer tubes.

The real answer is way more complicated of course. Forks of what length? What's the bike's mass? What's the grip loss point of the tyre fitted? etc. With all the possible variables there isn't a reliable figure for fork flex.

The only vaguely useful rough guide I've ever heard of (which ties in to the 10mm thing) is; for conventional forks you should be able to get your hand between the tyre and anything behind it (turbo, frame, headers) as the minimum. For USD forks you should be able to get your fingers all the way between the tyre and anything behind it. For a lightweight modern bike with large dia thin wall USD forks like a GSXR1000 then you should be able to get the tips of your fingers between the tyre and anything behind it.

Obviously that adds another variable, who's hand? but as it's a rough guide you're looking at an average.

[clivegto]

It's not a good idea if the front wheel can touch the turbo. Don't ask me how I know I just do  

[BillyR]

It really depends on the frame, something with less rake is always going to be tight.

A friend of mine with a slabbie turbo has a simple trick, to get good clearance on his front mount he just taped a section of 1.5" thick foam pipe insulation to the front tyre while he put it together.

Never had any problems.

[TLRS]

To add another variable.. speed. Might grow the tire a tiny bit.

Without having any realworld figures, 10mm seems plausible everything considered. Maybe someone curious with a running bike can do some tests. Video maybe or the foam?

[clivegto]