Air to Spring - why no easy comparison?

Im going to take a guess here - shock pumps vary and the average user is stupid.
If the purpose of the comparison is people buying springs based on the pressure they run, you’ll find a lot of upset people

Do frame manufacturers not provide a chart of recommended spring weights for rider weight?

As shocks vary, I guess the only party that could do this is the manufacturer of the specific air shock. And why would they.

Do frame manufacturers not provide a chart of recommended spring weights for rider weight?

Yep but only in specific springs... (ones they sell with the bikes)
TFT has me at just under 300lb/in.(firmer).. YT has me at 350ln/in that's a pretty big relative gap

The Select+ for one version says 195@30% and on the shred which has a coil option X2 @ 196 psi... and coil
350 lb/in...

I can get an orange SLS (£££) in 325lb/in but black (1/4 price) only in 300 or 350...

As above most people are stupid but having posted on manufacturer FB page 1/2 the people say too soft and half spot on... but would I trust someone who doesn't know the difference between a coil and airspring to tell me "spot on"??
It would be easier if TFT agreed but their calc seems to suggest I'd be 40 lb/in below so opposite of what user group are saying. (UK stock also seems a bit sparse)

My 1/2 arsed plan was to set up the airshock as per YT recommendations and see if its hard or soft for me... but that makes a huge assumption in that the two have been calculated in the same way by YT.

As shocks vary, I guess the only party that could do this is the manufacturer of the specific air shock. And why would they.

It makes commercial sense if they want to sell after market shocks... I find most mates who are coil curious it's the faffing about getting the right spring puts them off most?

What are you using to determine which coil

stevextc

As above most people are stupid but having posted on manufacturer FB page 1/2 the people say too soft and half spot on…

It would be easier if TFT agreed but their calc seems to suggest I’d be 40 lb/in below

You've kind of answered your own question there - it depends so much on rider, speed, trails, bike, personal taste, and other minor variablea like flat/clipped, etc One person't too soft is another's too harsh, it really is try it and see what works for you.

TF's calculater is a very rough starting point, I don't really trust it at all.

TF’s calculator has me bang-on with a 500lb spring (150mm rear travel and 57.5mm shock travel) I have 500, 600, 700 and 800 springs that came with the shock (I bought second hand)

I run the 600 with at least one full turn as the 500 is too soft. I could also run the 700 without any pre-load and can’t tell the difference if I’m honest.

So what I’m saying is that the calculated values can be off, but the difference I feel with 100lbs variation in the springs is small. Goose your starting point and go from there - it’s one of the reasons Pinkbike and eBay is full of people selling springs.

I found the tf tuned calculator for coil was miles out for me. Think it suggested 393lbs but the 500lb spring was needed in linear springs to avoid bottom out.

I tried a progressive 450-550 I think it was and didn’t love that - felt plush but then you hit an absolute wall of resistance towards the end. For me on my bike I bought a cascade link to up the progression through the stroke and it’s now amazing everywhere. So much better than the standard linkage with float x it came with. Even on the cascade link the air shock feels a bit wheezy compared to the coil.

I think everyone’s experience is a bit different - and shock tunes / having an hbo makes a big difference to what you can get away with.

Personally if you can use a Nukeproof of cane creek vault spring I’d use those whilst trying to find the weight you want as they’re a lot cheaper than fox sls and not much heavier. They sell on easily on ebay in my experience too.

bikerevivesheffield

TFT and the YT setup.... which give 300 (firmer) and 350lb/in ... which seems like a big difference at that end of the scale

TF’s calculator has me bang-on with a 500lb spring (150mm rear travel and 57.5mm shock travel) I have 500, 600, 700 and 800 springs that came with the shock (I bought second hand)

I run the 600 with at least one full turn as the 500 is too soft. I could also run the 700 without any pre-load and can’t tell the difference if I’m honest.

So what I’m saying is that the calculated values can be off, but the difference I feel with 100lbs variation in the springs is small. Goose your starting point and go from there – it’s one of the reasons Pinkbike and eBay is full of people selling springs.

Hmm... my experience was 50lb/in was a complete difference.
Different bike (mk1.5 Aeris)/linkage/shock but I had a 400 and 450 on my CC coil... 400 felt great on DH but bottomed out and on jumps there was just nothing to push against... I'd try and preload and ....

450 gave a nice platform to push against BUT I almost felt I might as well be running an airshock for the small bump...
I ended up with a 425lb/in which is TOTALLY goldilocks... It just feels awesome everywhere.

The MK2 Capra is very progressive... so to an extent I can maybe run softer at the top and get away with a bigger variation?

I found where I was on the calculator (also used TFTuned) and luckily for me, that's what came on the bike. Bought the next spring down after a few rides on it.  Did the same with the forks, but as the springs are "relatively" cheap, bought one up and one down from my starting point, and bracketed until I was happy and understood what the fork was doing, ended up with 2 spring weights down from recommended.

nickc

I found where I was on the calculator (also used TFTuned) and luckily for me, that’s what came on the bike. Bought the next spring down after a few rides on it. Did the same with the forks, but as the springs are “relatively” cheap, bought one up and one down from my starting point, and bracketed until I was happy and understood what the fork was doing, ended up with 2 spring weights down from recommended.

I bought a used eBay 350 (which is the YT recommended) and still waiting for delivery but meantime I finally got the rest of the bits together and took it on a test run. (Had to lengthen the vorsprung spring in the Zebs and various other swaps and stuff - kept the same spring as 160 for now**)

I used my fairly old RS pump and set the select + came with the frame to the recommended (146 psi and -7 rebound). I've not opened it up to check volume spacers but thought I'd check how the calculation for that went. Seemed a bit firm .. I have a specific huck to flat I repeat where I expect near 100% travel (mentioned in another thread) and I didn't get past 80% or so despite deliberately coming down rear first. Did the rest of the runs and jumps and the rear felt quite meh but then I'm comparing to the coil on the Bird or the air X2 on the eMTB.... but definitely smoother than on the HT 😉 so it was doing something.

When I got back to the pub I borrowed the shop pump and found I was about 155 psi but still have to determine if that was differences in pump or as I'd let a lot out transfer from the negative chamber I'd not equalised.

**Amuses me that I can get the smashpot spring to be correct by reducing my age (a lot). I'm not sure how that works on their spring calc 😉

Did the same with the forks, but as the springs are “relatively” cheap, bought one up and one down from my starting point, and bracketed until I was happy and understood what the fork was doing, ended up with 2 spring weights down from recommended.

I'm coil-curious. Obviously swapping shock springs is a doddle but looking at smashpot installation videos there seems to be a bit more faff - how does that work in practice? Similar faff to an air spring service or more?

@thepurist

I’m coil-curious. Obviously swapping shock springs is a doddle but looking at smashpot installation videos there seems to be a bit more faff – how does that work in practice? Similar faff to an air spring service or more?

It's different... no harder but caveats. It's one of those things it's more obvious when you are holding the stuff in your hands rather than watching a video.

Changing the spring only can be done without taking the lowers off....
BIG caveat - applies to Zeb's and older style kits with a plastic spacing but this is replaced by a integrated sleeve/spring perch in newer kits. (If you don't have a Zeb or get an older style kit it's fine but the protective plastic spacing is VERY VERY tight on the Zeb and this makes it more faff/tricky) {38's had the same but nowhere near as tight}

It's probably closer to adding a volume spacer/token in a airfork just a lot messier. Remove topcap... pull spring out .. put new spring on and replace top cap. Copious amounts of grease and oil though!

HOWEVER
Changing travel however is more involved... involves removing the entire assembly, heatshrink and adding/removing 2 sets of spacers and you have to crack the seal on the lowers.

I'd just changed oil / wipers so I did mine yesterday without completely removing the lowers... recovered 100/110ml of 20wt.. and the heatshrink came off non destructively and went back on then reheated. New grease/topped 10ml of oil and replaced. Not a big job but a lot messier.

Something to bear in mind when looking at spring calculators etc is that the rates for springs for mtb are really not much more than notional on all but the very pricey and our heavy ones.

It's easy to say a "XYZ recommended a 450lb spring but that was terrible so I put a 500 on and that was great" but there's a very good chance the 450lb one was actually about 410lb and the 500 is actually 470 (or 550) so the calculator was right it's just the spring is rubbish*.

You could put three 450lb sls springs on one after another and get massively different rides out of all three despite their being the same.

As ever it's a problem of chasing weight on things which are inherently not light.

Of course how you ride (northwind mentions this on the trail fork thread) also has a huge impact on how good the numbers will be for you.

When I last ordered a spring from TF the tech asked loads of questions about riding style before recommending a weight.

In short, it's not a simple comparison.
Depending on how the shock to suspension travel ratio varies through the suspension travel, you can require some very different values.

If you have a bike linkage designed so that it compensates for a non-linear air shock to maintain a linear suspension force through it's travel, then by switching to a coil, you then need to run a harder spring to avoid excess bottom out.

At the other extreme where you have a suspension designed to ramp up throughout the travel to make the most of a coil shock, you need to run an air shock at a relatively low pressure.

There used to be a couple websites where you could see how different suspension designs affected the ratios, but I don't think they went as far as running calculations on shock forces, and I can't even remember what the websites were to check.