Lightening 26R Style Chassis

[stevebroad]

[quote="stevebroad We are running 800lb fronts with helpers (they may not be needed once car is assembled) and 400lb rears with 450lb tenders. We hope to run without ARBs by using droop limiters. Don't ask me how it works, I am just doing what my suspension guru tells me

Steve

The spring rate of the chassis is lower than that of your suspension . You must have smooth tracks and love racing go carts

cheers
Rohan[/quote]


Chassis is a LOT stiffer than standard. Car is designed specifically for drag racing with sprinting as a side line. Spring rates have to take into account weight of engine and rear transmission which are a lot heavier than standard.

Pudding, proof, etc

Regards
Steve

[stevebroad]

Steve, I only upped the caster by one degree, which was easily done by fitting thick and thin alloy spacers to get the bottom wishbones fully forward and the top ones fully back. Keep in mind the rose joints are much narrower than the original bushes. I don't think I am stressing the trunnion as everything is very free with the springs removed. I used to use Canley Classic trunnionless uprights, but the mounting angle with the cranked bones was causing "necking" in the joint.

Alan Pate

I am using the Canley uprights, Alan, modified to accept Spyder style bottom wishbones with, fortunately, no binding isssues. I threaded the whole length of the top wishbone studs so that, with a nut each side of the rod end, caster can be easily adjusted without having to take it apart.

There is a hell of a caster range stated in my manual, 7 degrees between 26/3001 to 26/3061 then 3 degrees thereafter. Don't know how caster angle was changed by the factory.

The uprights are not exactly a close fit in the trunnions so going from 3 to 4 degress (I am guessing washers with around 2mm thickness difference?) is probably well within the slack in the joint

Steve

[msd1107]

It is amazing how much the nuts and bolts in a complete car weigh. So, there is much room for savings. Try any or all of the following suggestions, or come up with some more.

Look at the fixing torque for the nut/bolt. Calculate the stress on the threads and shanks. If the stresses are less than what aluminum can withstand, use replacement aluminum ones. This saves 2/3 straight away.

If you are using lock washers, use self locking nuts, safety wire the nuts, or use a locking gel or some form of LockTite..

Source nuts 1/8 or 1/16 smaller and tap them out to standard size.

Source 1/2 height nuts (if there are enough threads engaged).

Measure how far the bolt protrudes from the engaging nut. Source a bolt whose length is barely longer than what is necessary to fully engage the nut (or else cut the bolt to length and re-cut the thread).

Source 1/2 height Allen head bolts (or thin the bolt heads and drill the center). (note: for thin headed bolts and nuts, you probably want to use 6 point sockets).

Depending on how the bolt is used, waist the bolt shank (some bolts can be sourced already waisted) or drill the bolt shank so the calculated torque is below the yield strength of the bolt.

If you are still using knock-on wheels, convert to bolt-on and follow all the above. Lighter wheels provide a better ride and require a lower spring rate.

Everybody add their favorite weight reducing technique.

David
1968 36/7988

[stevebroad]

Look at the fixing torque for the nut/bolt. Calculate the stress on the threads and shanks. If the stresses are less than what aluminum can withstand, use replacement aluminum ones. This saves 2/3 straight away.

If you are using lock washers, use self locking nuts, safety wire the nuts, or use a locking gel or some form of LockTite..

Source nuts 1/8 or 1/16 smaller and tap them out to standard size.

Source 1/2 height nuts (if there are enough threads engaged).

Measure how far the bolt protrudes from the engaging nut. Source a bolt whose length is barely longer than what is necessary to fully engage the nut (or else cut the bolt to length and re-cut the thread).

Source 1/2 height Allen head bolts (or thin the bolt heads and drill the center). (note: for thin headed bolts and nuts, you probably want to use 6 point sockets).

Depending on how the bolt is used, waist the bolt shank (some bolts can be sourced already waisted) or drill the bolt shank so the calculated torque is below the yield strength of the bolt.

David
1968 36/7988

I use aluminium bolts wherever possible.

I will use titanium wheel nuts saving around 40%.of rotational mass. Saving on rotational mass is always good.

Lock washers are usually a waste of time and weight. I use half height nylocks with 1 1/2 threads protruding .
I turn down bolt heads and centre drill where safe to do so. Not keen on wasting shanks as this is where most of the strengh lies. I leave suspension bolts alone apart from slight skimming of head and keeping length to a minimum.

I like to have a bolt thread engagement of a minimum of 1 1/2 times the bolt diameter. EG for a 10mm bolt 15mm of thread engagement. This is nowhere near the recommended minimum but I feel comfortable with this extra margin of safety.

One racing trick I am using, but you will need an understanding MOT man if car is to be used on the UK highways, is to use only 3 bolts on a 6 bolt CV jonit. The other three are replaced with short studs that engage only with the first flange. The stresses are sheer only and you still have 6 sheer resisting points. This saves around 35-40% of the rotational bolt mass.

[rgh0]

In theory you only need to fully engage 3 threads in standard bolt thread designs to be able to develop the full strength of the bolt. This however requires thread engagement to be perfect between the nut and the bolt. In practice you need some more engagement which is why nuts are deeper than 3 threads. But if you want to save weight push the thread engagement down to 3 threads. I however would not do the experimenting on my con rods bolts .

cheers
Rohan

[stevebroad]

In theory you only need to fully engage 3 threads in standard bolt thread designs to be able to develop the full strength of the bolt. This however requires thread engagement to be perfect between the nut and the bolt. In practice you need some more engagement which is why nuts are deeper than 3 threads. But if you want to save weight push the thread engagement down to 3 threads. I however would not do the experimenting on my con rods bolts .

cheers
Rohan

Yes, 3 threads is great on paper, but even an anal weight freak like me would blanche as the thought of going that close to the limit. 1 1/2 to 2 bolt diameters seems fine to me when fitting a bolt into a blind hole. However, I am quite happy to use half nuts which are less than 1 bolt diameter. I will have to think about that ::-) I have left all the engine bolts alone.

[elandoc]

Bugger me!
And I thought I was anal!
BTW, try drilling out the ignition key - lots of spare metal there...

[stevebroad]

Bugger me!
And I thought I was anal!
BTW, try drilling out the ignition key - lots of spare metal there...

I hadn't thought of that. Drill a hole in the handle part of the key and perhaps run it through the mill in order to reduce its thickness.

[Davidb]

I have resurrected this old thread because a/ it is interesting and 2/ I want to ask a question relevant to this thread.

I ordered a rear 26R knock-on hub from Kelsport and they asked if I wanted steel or aluminium. The aluminium would be far cheaper to ship he thought. I thought about it and decided that the idea of an aluminium hub, pressed onto a tapered steel shaft, undergoing both heat and load variations was not a good recipe-I could see fretting occurring. So I ordered the steel hub.
My god it is heavy!-Slightly over 2kg. Is anybody using the alloy rear hubs and can report on them?

[elandoc]

David, I machined my own chrome-moly rear hubs. I also converted from 5 peg knock-ons to bolt-ons for safety, but I think it's a bit lighter.

[Davidb]

I admire your skill! I have a small lathe but I would not risk my life with something I had machined!

Any thoughts on the aluminium rear hubs for the 26R?

[elandoc]

My fronts are 7075 T6 alloy - very strong, but I think a well thought out chrome moly drive hub for the rear is best. I removed a lot of unsprung weight by switching to alloy calipers (Wilwood), 4 pot on the front, 2 pot on the rear, although next time I'll put 4 pot all around with a limiting valve - I think I'm giving up some rear bias, especially in the wet. I have to have a handbrake for scrutineering, so I installed mountain bike calipers - 120g each!

Oh, and the only skill I displayed was signing the cheque!

[Davidb]

Anybody else have an opinion on alloy rear hubs for a 26R installation?

[rgh0]

A proper T6 temper alloy billet has comparable yield and UTS strength the the original cast iron hubs. It is a little softer and will tend to fret more so its life will probably be less than a cast iron hub or steel replacement. The elastic modulus is less so it will stretch a little more and move inwards a little more as you bolt it onto the taper.

I dont see any reason not to try it. If it does not work then replace it and the Lotus community will have learned something ? That's what development is all about.

cheers
Rohan

[Davidb]

Can we use your money for this 'experiment' Rohan?