Hi

I'm looking for some cheap forks (about £60-80) but I can't seem to find anything that fits the bill. I've been looking at these and I almost bought them, but then I saw the brake mounts. These are post mount and I need International Standard at 160mm (I'm guessing size matters here). No matter how hard I look I can't find any Suntour forks of about this price range with the right mounts!

I also need it to have a steerer tube of 1 1/8th width and a steerer tube of at least 210mm.

Cheers

What brake do you have ?

There is this 160mm adapter that will allow a IS brake to be fitted to a PM fork.

*Not all IS brakes can be used with this adapter.

Any fork for that money will be a budget fork, ok if using on road, but will only last a short while if using off road, you need to be looking at the £150-200 for the start of anything decent for off road use.

For the mounts, IS is becoming obsolete for forks, with most manufactures now using the Post mount system, are you sure your calipers are not Post mouts, as most disc calipers are now Post mounted, with IS adaptors for older forks (5+ years old).

For the size, most forks will be 1 1/8th, you will find very few 1 inch forks, and if tapered or 1.5 it they will be higher end. also, if new, they should be un-cut, and will be longer than the 210mm you need

I have no idea what my brakes are. They don't say. There's a link to the bike in my signature, but I don't think that'll help much cos it doesn't say much about them.

Why would I not be able to use all IS brakes with this thing?

Cheers,

Post mounts mount from the back, and IS from the side, right?

Yes, have a look at this tech doc, this shows what the 2 mount types look like https://techdocs.shimano.com/media/te...9830682460.pdf

The brake on that bike in the link is Post Mount.

Some IS brakes won't work with that adapter because of the physical size of them, the IS brake when attached to that adapter ends up being positioned between the post mounts on the fork, some IS brakes are just too big to fit between the post mounts.

Spinner and other Brands ship out at lower price points ..

Aha! You're right Cobba - the thing that threw me was the fact that the forks (and the tabs on the rear of the bike) are IS, while the calipers are PM. So, can I just go straight to a PM now? The thing that confuses me is that the adaptor used adds a good deal of thickness to it, so wouldn't it have to have the disc moved?

Cheers!

PS Here's a macro shot, just to make things clearer

So much for the macro shot:
https://s1002.photobucket.com/albums/...3DCIMG4714.jpg

Yes, with a 160mm rotor the brake you have will bolt directly onto a PM fork minus the adapter that's currently on it.
You would only need adapters if you put on a larger size rotor.

You'll need to find the specs for post mount spacing to compare to your caliper but generally calipers are all post mount with adapters to make them work with IS mounts. Your caliper is one of these. If you unscrew the caliper itself from the shallow cradle like adapter that actually bolts to the mount on the fork the resulting bare caliper will fit onto a post mount fork and be in the proper position and spacing to fit the standard small disc size of 160mm.

And the guys are right that those Suntour forks won't be any sort of upgrade. If you're just looking at a replacement then fine. But an upgrade they are not.

It's fine for them to be a replacement - as long as they have more travel than the original ones, which are listed as being 50mm travel. Regardless, it still confuses me - do I just need to align the front wheel over a bit?

Sorry I'm being thick here!

No.

The post mounts on a post mount fork are positioned further inwards then the IS mounts on a IS fork. The brake will end up being in same position on a PM fork as they were on the IS fork with the adapter.

A 100mm travel fork should be OK on your bike, it's probably not a good idea to get a fork with any more travel then that.

Now that makes sense! Besides, I only weigh 115 pounds so it can't go too far!

Cheers for all the help!

One last question: These (https://cgi.ebay.co.uk/Suntour-XCR-LO...ht_2379wt_1270) say that they are geared up for a 180mm rotor. I have a 160mm. Is that OK, or do I need to be looking for others?

Cheers

Edit.

That fork seems to have post mounts for a 180/185mm rotor.

You need one with 160mm post mounts unless you want to put a bigger rotor on it.

I thought that the 180mm was a typo and it should of read 160mm till I looked at the specs on the SR-Suntour website.

...but it then says "Maximum Disc Rotor Diameter: 185mm". Is that then the absolute maximum?

Edit above.

Awesome, thanks. That clears that up!

You may want to re-think and go with an 85mm fork. The difference in axle to crown between a 50mm travel fork and a 100 is going to be quite large. It will lift up the front of your frame a lot more than the designers intended and could easily make your steering feel "floppy" at lower speeds due to the change in the steering geometry that raising the head tube will cause. Generally longer forks of 100mm's or more travel shoudl be used on frames with higher located steering head tubes intended for use with such forks.

Some forks on the Suntour website say the travel is "80,100,120". Would that solve the problem?

Not really. Unless they are some top level fork it means that they are available in models with one of those travels. But you would still need to stay with the shorter 80mm travel. And even if you did get some top end model with selectable travel you would be limited to using the shorter travel length so it didn't lift up as high.

You see, all forks will collapse down under full compression to about the same distance. That being limited by the clearance needed between the lower side of the crown to the axle for the wheel and tire and the cross bridge of the fork. So to get longer travel they need to make the extended length longer. And that means it lifts up the crown and the frame needs to be designed to work with a fork that has the crown that high up. Your frame was designed to use either a rigid fork or a short travel suspension fork. You can no more put a long travel fork on your frame than a downhill bike intended to be used with 130 to 150mm double crown forks can put a short 50mm travel fork on and still ride properly.

The final limiting factor is that you don't want to increase the axle to crown distance by more than maybe 20 to 30mm. Even that much will have an effect but likely it won't be too much to mess things up totally. But when you're looking at a 50mm or more increase in the axle to crown distance you can expect the bike to handle poorly with such a change.

Yikes, now you've scared me! I enjoy the bike's handling as is but better forks would be nice. Is it really going to screw it up that badly? Considering it's the Landy MTB in my signature, link there too.

Well, the reduction in idea feel is directly proportional to how much longer over the original spec you make the forks. As I typed in the last reply you can get away with 20 to 30mm of longer fork but when you start going over 30 and range up to 50mm longer than what you have now then you're certainly going to feel the difference. And it's not going to be a good difference.

And the brand doesn't make any difference. It's just the way the frames are designed to have the correct steering geometry when used with a narrow range of fork lengths. Some frames, like yours, need shorter forks and others, like more expensive all mountain or downhill bikes, need long forks.

In your case you can pretty easily say that an 85mm travel fork won't ruin your handling. You will feel some effect but it'll just be "different" and not "bad". But put a 100mm fork on there and the results will likely not be that nice.