Rear suspension travel

[Purplemeanie]

Can someone tell me what sort of rear suspension travel I can expect on a Seven?

Assume the car is set to a "normal' ride height and on standard factory springs/dampers (assume adjustable Bilsteins, but not the newest ones fitted to the 420 Cup). The car is an SV if makes any difference.

I'm asking so I can work out how high the de-dion tube will travel under full suspension compression. 

I guess another way of asking the question is - if you assume the rear suspension bottom's out when the de-dion tube hits the chassis tube-work, how high can the de-dion travel above that lower point?

And what's the practical limit, as I assume most cars are sprung stiffly enough that they never reach the theoretical maximum compression (or is that assumption wrong?).

Thanks, John

[7 wonders of the world]

Hi John,

Might be worth placing a wanted add for a pair of old rear dampers so you can build without springs and do real time simulations, I had a very old pair but looks like I binned them.

Spring rate wise you will find 130 - 150lb linear springs are pretty common for the rear, although the stock CC SV springs are progressive

I normally move the bumps stops down the damper shaft in order to check and I reach full compression occasionally on the road and I'm running 150 rears - no comments about too many pies please.. 

[Purplemeanie]

Thanks Neil. So, have you any idea what the amount of travel is when you hit your adjusted end stops?

I'm going to take the dampers off my project car and do some tests, but in the short term I wondered if anyone had a rough idea of what the upper most travel would be.

If nobody has any quick thoughts then I'll give Meteor a call and bug Simon, I'm sure he'll know.

John

[AlastairA]

John - one idea taken from mountain biking experience would be to attach a tie wrap to one the shafts on one of the dampers such that it gets pushed up as the damper works - and stays at the maximum travel. Although the upper part of the coil is quite closely wound, I would think it might be possible to get a tie wrap in there. At least this would give you some accurate empirical data after a stiff drive.

Alastair

[7 wonders of the world]

Hi John

Just had a measure whilst I was out in the garage

Top of lower chassis rail to underside of dedion tube is 55mm

Travel 100mm

Latest imperial chassis with latest dedion tube and Protech rear dampers you might get slight variations between brands

Hope this helps

 

[Purplemeanie]

Thanks for all the feedback chaps 

I clearly need to take a damper off and play around with it.

John

[Gridgway]

Just curious about why you need to know?

Should be fairly easy to pull a damper off, take off the spring and measure the closed length?

[Purplemeanie]

Yep, its not a lot of agro to do a measurement, I just thought it would be something that someone knew off the top of their head. ¯_(ツ)_/¯ 

I need to know the extent of travel as I'm looking to put something else where the diff would normally be and I'd like to know if the de-dion tube could hit it.

John

[Gridgway]

in which case, being quite important, I'd refit both dampers without springs (with any bump stops) and jack up the DD tube to see where it goes.  I'd not rely on others' measurments as there may be differences, damper closed length for example.

When addinf a facet fuel pump to the rear of my LA caterham, I did exaclty that, not wanting a axle-fuel pump interface moment!

[Purplemeanie]

Thanks Gridway, I may do exactly that but for the moment I took a damper off and measured the length of the piston between the bump-stop and the bottom of the piston. That measurement was (within my parallax capacity) 100mm. So, my rough measurement means the de-dion tube can travel a maximum of 100mm from the top of the chassis tube to its bumb stops - that was the measurement I was after.

See images extracted damper and tape measure below...

(side note: the damper and spring were actually fully extended with the de-dion tube touching the chassis tubes).