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XI with an R1 bike engine


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On 05/08/2020 at 10:07, Morris said:

The axle for wire wheels is narrower from what I recall.

Yes it is, fitting wire wheel half shafts into a steel wheel axle is a great way to ensure that the spline snaps off right at the end leaving you to have to remove the diff to extract the broken pieces.  

 

The half shafts have a habit of snapping like carrots at the spline.  I believe that this is because the shaft is machined from a single diameter piece of steel.  This means that the spline is the narrowest point along the length.  For my car I had the shaft machined along its length, this spread the torque load along the whole shaft not concentrate it at a single point.

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When I had my XI on a handling circuit it was the best fun I have ever had.  On the hard skinny 155 tyres fitted to wire wheels it was proper fun.   On my car the front end was very pointy,

I'm also a huge fan of 'road' tyres for track use, particularly on light cars.   As MK11 says, they are a lot of fun, with a wide operating range from grip to slip, wear surprisingly slowly,

This is where the engine will sit, the sump is flush with the gearbox hoop, even though it looks a lot lower! The silvery cookiebox thingy is actually the Oil cooler! It's cooled with the coolant, s

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Ortekk

A lot of work, with almost nothing to show for it the last few weeks, but I've installed the reverse box, which was a very very tight squeeze, and also welded on the mounting points to the now correct(!) rear axle. Differential rebuild is in the works, but I need to practice my black magic to get it right. And make my own shims so I don't have to destroy the bearings when I get it wrong.

Also remade the engine mounts so they're properly supported. Just need to weld everything together. 

I've not had to motivation to take any pictures, it's riveting stuff spending 8h grinding 0.89mm of both sides of a support so the reverse box fits... I'll do a proper update next weekend :)

Now I'm shopping for rims! And I need some knowledge and advice to help me here, as I know next to nothing about rims, So I have tons of questions here...

I'm planning to run 175 wide tires in the front, and 185 in the rear. So 5.5J and 6J rims sounds reasonable... But what offset do I need?
I'm in a bit of a pickle since the bodywork is stored in another location, so I can't just pop it on and measure how much room I have.

Am I correct in thinking that 6J are too wide for the front? Should I need wider rims to provide support for the tires at the rear? The camber is 0, so it seems likely that the tire will fold during heavy cornering, especially if I mount sticky tires.

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Simon Marks - North Oxfordshire AO

Your rim widths sound fine.  My Talbot Sunbeam Lotus came with 6J rims and 185/70x13 tyres.  I run 185/60 tyres on that car with no problems - and the tyres do not look like they are having a hard time on the various photos I have when sprinting (often sideways).  On my Westfield XI, I have 5J rims and 165/70x13 tyres.  My Sierra Sapphire Cosworth has 7J rims and 205 wide tyres - so follows the mathematical series!

 

I'm afraid that I have no idea on offset though the rims on my XI are GB Minilite copies specified for a normal MG Midget.

 

On 13" wheels, there seems to be plenty room at the front.  I built my car with the rack limiter spacers as the build guide and ended up with a H_U_G_E turning circle.  I have since removed them without issue.

 

Simon

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Ortekk

I thought about getting a pair of Minilites, but I really want Force racings Mesh rims. They look fantastic imo!

Good to know that I got the width correct. Interestingly, Force racing wants me to go 6J on the 175 tires as well. Though I think they want a bit more support for the front tire, which I've read is normal.

But the drawback with custom rims is that I need all of the measurements, 13" and 5.5J doesn't say where the center should be 😛
The Minilites for the Midget says +20 offset, do you think I should go with that both front and rear, or should I have different offsets?

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